Heat pumps are well known and used for heating and/or cooling enclosures such as buildings and the like. A heat pump generally includes a heat exchanger fluid (usually called a refrigerant) that is circulated between an interior heat exchanger inside the enclosure and an exterior heat exchanger outside the enclosure.
During normal heating mode operation of a heat pump, the exterior (outdoor) heat exchanger thereof becomes colder than exterior ambient and absorbs heat into the refrigerant therefrom, and the interior (indoor) heat exchanger becomes warmer than interior ambient, transferring heat from the refrigerant into the indoor air. Thus, heat is xe2x80x9cpumpedxe2x80x9d from a cooler exterior ambient into an interior ambient.
When the exterior temperature is near or below the freezing point of water, generally in the range of 30 to 40 degrees Fahrenheit, ice (frost) usually builds up on the exterior heat exchanger, greatly reducing the heat pump performance. Therefore, defrosting means are generally employed in heat pump systems. During these outdoor conditions, heat pumps using thermal expansion valves (TXV) instead of orifice-type expansion devices throttle the flow of refrigerant and prevent the heat pump from operating at optimal conditions for heat transfer.
The use of heat pump reversing defrost systems in heat pumps is well known. Such defrost systems are generally designed to melt ice build-up and evaporate water from the exterior heat exchanger in order to minimize deleterious effects of ice on the heat exchange process. Such defrost systems generally activate after a period of heat pump run time, and generally operate until the exterior heat exchanger is raised to a certain temperature to ensure removal of all or at least most ice and water.
During the defrost cycle, the heat pump is generally reversed. The exterior heat exchanger becomes warm, and the interior heat exchanger becomes cold. An auxiliary interior heater (usually an electrical resistance heater or a combustion heater) is energized in order to compensate for the heat absorbed during the defrost cycle by the interior heat exchanger.
In case the heat pump heating capacity cannot meet the house heating load requirement, conventional heat pumps energize the auxiliary resistance heating coil to meet the required load. This can cause a large interior temperature swing, and lowers the efficiency of operation.
The present invention relates to heat pumps having thermal expansion valves (TXV) and cyclic defrost systems, and more particularly to such heat pumps which employ a means for reducing the frequency, duration, and energy consumption of the defrost cycles by modulating the TXV during frost-prone outdoor conditions thereby increasing interior (indoor) thermal comfort.
In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a heat pump system comprising, in an operable relationship for transferring heat between an exterior atmosphere and an interior atmosphere via a fluid refrigerant: a compressor; an interior heat exchanger; an exterior heat exchanger; a heat pump reversing valve; an accumulator; a thermal expansion valve having a remote sensing bulb disposed in heat transferable contact with the refrigerant piping section between said accumulator and said reversing valve; an outdoor temperature sensor; and a first means for heating said remote sensing bulb in response to said outdoor temperature sensor thereby opening said thermal expansion valve to raise suction pressure in order to mitigate defrosting of said exterior heat exchanger wherein said heat pump continues to operate in a heating mode.
In accordance with another aspect of the present invention, a method of heating an enclosure includes the steps of:
a. providing a heat pump system comprising, in an operable relationship for transferring heat between an exterior atmosphere and an interior atmosphere via a fluid refrigerant: a compressor; an interior heat exchanger; an exterior heat exchanger; a heat pump reversing valve; an accumulator; a thermal expansion valve having a remote sensing bulb; an outdoor temperature sensor; and a first means for heating said remote sensing bulb in response to said outdoor temperature sensor;
b. operating said heat pump in said heating mode;
c. intermittently operating a defrost mitigation cycle comprising maintaining said heat pump in heating mode while energizing said first means for heating said remote sensing bulb in response to said outdoor temperature sensor to fully open said thermal expansion valve and raise suction pressure in order to mitigate defrosting of said exterior heat exchanger.
Accordingly, it is an advantage of the present invention to provide a heat pump having new and improved defrost mitigation cycle system. It is another advantage of the present invention to provide a heat pump defrost mitigation cycle system which significantly reduces the frequency of heat pump reversing. It is a further advantage of the present invention to provide a heat pump defrost mitigation cycle system which significantly improves interior thermal comfort during the defrost cycle. It is a further advantage of the present invention to provide a heat pump defrost mitigation cycle system which significantly improves the reliability of the heat pump. It is a further advantage of the present invention provide a heat pump defrost mitigation cycle system which saves a significant amount of energy during operation of the heat pump.
Further and other objects of the present invention will become apparent from the description contained herein.